Typical municipal and industrial wastewater streams contain solid particles in a range of sizes and densities. During conventional treatment processes, solids of larger sizes and densities are removed from the waste stream rather easily. Often, as a primary treatment step, the wastewater is detained in a basin where the heavier particles (those having a density greater than the fluid medium carrying them) settle out of the waste stream through the effects of gravity. Smaller and/or lighter solids, however, remain suspended in the waste stream requiring additional physical and/or chemical processing for removal. Secondary treatment processes designed to remove additional settleable solids commonly include chemical addition of long chain polymer compounds, followed by coagulation, flocculation and solids separation steps.
In both primary and secondary treatment phases, the settled solids are collected (typically at the bottom of the treatment basin) into sloped channels where they naturally thicken near a solids collection manifold. The collection manifold is commonly a perforated channel or conduit in fluid communication with a pump or other means of creating a hydraulic gradient differential between the manifold and the collected solids. In this configuration, solids can be removed from the treatment chamber without disrupting the treatment process. Non-invasive solids removal processes such as this are desirable because they reduce or eliminate the need for physical and mechanical solids removal equipment which results in lower installation and maintenance costs for the treatment unit. In addition, physical and mechanical solids removal procedures require the treatment basin to be periodically taken out of service and/or reduce the amount of wastewater that can be treated in a given period of time.
In order for in-line solids removal processes to function effectively, the solids must be in a fluidized state so as to be drawn into the collection manifold. It is a known problem that accumulated solids, particularly those that include chemical coagulants, thicken above the collection manifold and resist resuspension without physical or mechanical assistance. With a collection manifold that is covered with viscous solids, the pressure differential may only create local pockets of solids fluidization above the collection ports. This condition creates a “rathole” effect that results in reduced solids removal rates and creates a solids build-up that resists non-invasive removal. In addition, the removed solids stream has a solids concentration that is undesirably low thereby requiring greater thickening and disposal costs.
It is therefore a problem with some conventional in-line solids removal systems that settled solids cannot be adequately resuspended to be withdrawn through a collection manifold without the aid of mechanical scrapers, agitators or similar physical aids. It is a further problem that the fluidized solids that are removed in such systems have low solids concentration rates that result in higher costs for solids handling and removal.
The following inventions describe enhancements to an in-line solids removal process that improve solids resuspension without the application of physical scrapers or mechanical agitators. The inventions describe various means to create transient pressure waves in the collection manifold. The transient pressure waves operate in a manner similar to the water hammer effect known in the art. Under the water hammer effect, a fluid stream in motion in a closed conduit has a momentum head. When the conduit closes (as with the operation of an in-line valve) the momentum head reflects off the closure and creates a pressure surge that travels back through the conduit. The pressure surge returns to the closure and back through the conduit repeatedly until the pressure surge is dampened. In the proper frequency range, the pressure waves improve resuspension of solids and reduce “rathole” effects. Therefore it is a feature and an advantage of the inventions that settled solids can be resuspended for removal without the use of mechanical scrapers or agitators.
It is also a feature and an advantage of the inventions that chemically conditioned solids that cannot be removed by conventional in-line systems can be removed by the pulsating flow regime without the aid of mechanical scraping or agitating. It is also an advantage that similar results may be obtained through air scouring of the collection manifold, either alone or in combination with a transient pressure wave.
Definition of Terms
The following terms are used in the claims of the patent and are intended to have their broadest meaning consistent with the requirements of law:                wastewater: any municipal, commercial or industrial process water not intended for human ingestion.        
Where alternative meanings are possible, the broadest meaning is intended. All words in the claims are intended to be used in the normal, customary usage of grammar and the English language.